1. Field of the Invention
The present invention relates to a printer that handles sheets of paper, and more particularly, to a point of sale (POS) printer for printing on sheets of paper, such as, for example, paper slips, bank checks and the like.
2. Description of Related Art
A POP printer typically uses an impact dot method or an ink jet method to print on a sheet of recording paper, and may be used to print on a single sheet of paper (herein after referred to as a cut sheet of paper), such as, for example, a paper voucher, a slip, a bank check or the like. Typically, the printer has a cut-sheet feeding aperture for inserting a cut sheet of paper in the printer. The cut sheet of paper is transferred by rollers disposed adjacent to the cut-sheet feeding aperture to a printing section within the printer. The cut sheet of paper is printed at the printing section and then discharged from the printer through a discharge aperture by the operation of rollers that are disposed adjacent to the discharge aperture. Upon inserting a cut sheet of paper through the cut-sheet feeding aperture, the rollers disposed adjacent to the cut-sheet feeding aperture are separated from each other to facilitate insertion of the cut sheet of paper.
When a calculation result or the like is printed on a relatively large sheet of paper, such as a slip, (herein after referred to as slip printing), using the above-described paper feed path for transferring cut sheets of paper, the slip of paper is transferred through a paper feed path in the following manner. The slip of paper is inserted in the cut-sheet feeding aperture used for slip printing, passed through the printing section, and discharged from the discharge aperture used for slip printing.
On the other hand, the same printer may be used in a different printing operation mode. When printing five or six lines in a predetermined area on a card-shaped sheet of paper such as a bank check for payment validation (herein after referred to as validation printing), the card-shaped sheet of paper is inserted through the discharge aperture used for slip printing to the deepest section of the printing section. Then, the lines are printed on the card-shaped sheet of paper while the card-shaped sheet of paper is transferred back toward the discharge aperture.
For example, FIG. 9 shows an explanatory view of a conventional printer that is capable of validation printing. A print head 4 performs printing on a single slip of paper or a cut sheet of validation paper 500 which is transferred onto a platen 38 by a pair of transfer rollers 19 and 20 and a pair of transfer rollers 21 and 22. The transfer rollers in each pair can open and close with respect to one another.
For printing on a slip of paper 500, the slip of paper 500 is transferred through a slip paper feed path 501. More specifically, the slip of paper 500 is inserted through a sheet insertion aperture 510 defined in the front surface of the printer. Then, the slip of paper 500 is guided by a paper guide 39 onto the platen 38, printed by the print head 4 and discharged through a discharge aperture 520 defined in an upper area of the printer.
When printing on a cut sheet of validation paper 500, the transfer rollers 19 and 20 and the intermediate transfer rollers 21 and 22 are both separated from each other as shown in FIG. 9. After, the cut sheet of validation paper 500 is inserted into a groove section 501a, the transfer rollers 19 and 20 and the transfer rollers 21 and 22 are both brought into pressure contact to pinch the cut sheet of validation paper 500. While the cut sheet of validation paper 500 is transferred upwardly toward the discharge aperture 520, the print head 4 prints on the cut sheet of validation paper 500.
The above-described printer suffers from the following problems.
(a) In order to insert a sheet of paper in a variety of forms in the cut paper feed path, the rollers at the insertion side are preferably separated from each other for slip printing and the rollers at the discharge side are preferably separated from each other for validation printing. In a conventional paper feed mechanism of the printer for printing cut sheets of paper, opening and closing of the rollers at the cut sheet insertion side and opening and closing of the rollers at the cut sheet discharge side are independently performed by different power sources (plungers or the like). As a result, the mechanism is complicated and independent control circuits are required for the respective power sources. Furthermore, the printer shown in FIG. 9 requires an additional mechanism for opening and closing the intermediate transfer rollers 21 and 22 in addition to the mechanism for the rollers 19 and 20 at the cut sheet paper discharge side to allow insertion of the cut sheet of validation paper 500.
(b) In the POS printer of the type described above, a sheet of paper must be inserted in an appropriate aperture depending on the specified purpose and use. Therefore, the POS printer may have a plurality of apertures for inserting and discharging sheets of paper. In some cases, one aperture may be commonly used for inserting and discharging sheets of paper. As a result, sheets of paper can be wrongly inserted by mistake.
There is another type of POS printer that prints on a sheet of recording paper in a roll (herein after referred to as a rolled sheet of paper) for printing receipts in addition to printing on a cut sheet of paper. In this type of POS printer, a portion of the paper feed path for cut sheets of paper is used as a paper feed path for the rolled sheet of paper, and each type of paper is transferred to a common printing section. As described above, the paper feed path is formed in a manner that each different type of paper is transferred to a different discharging aperture. As a consequence, the number of apertures for inserting and discharging sheets of paper is increased, and more errors during operation and insertion are likely to occur.
(c) In general, sheets of validation paper may have a variety of different qualities. For example, there are thick, sturdy sheets of paper, thin, weak sheets of paper, copy papers formed from a plurality of laminated thin sheets of paper and the like. In order to smoothly insert and transfer a sheet of validation paper that may vary in qualities, shapes and types, a transfer path for the validation paper is preferably formed straight. In order to form a straight paper feed path, a straight groove section, such as the groove 501a of FIG. 9, must be formed for positioning the bottom edge of the validation paper, as shown in FIG. 9, in addition to the paper feed path 501 for transferring slips of paper.
When the paper feed path is formed in this manner and if the sheet of validation paper is curved, the sheet of the validation paper may not correctly enter the groove section 501a, and may instead enter the slip paper feed path 501 for transferring slips of paper, as shown in the broken line in FIG. 9. If printing is started with a sheet of validation paper being set at a wrong position, then the initial position of the sheet of validation paper deviates from the designed initial position, and therefore printing may not likely be performed at a specified location. Accordingly, a mechanism for preventing such a problem may be additionally required, and thus the paper feed system and the control of the paper feed system become more complicated.